Highly Selective Hydrogenation of Biomass-Derived Furfural into

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Highly Selective Hydrogenation of Biomass- Derived Furfural into Furfuryl Alcohol using a Novel Magnetic Nanoparticles Catalyst Ahmed Halilu, Tammar Hussein Ali, Abdulazeez Yusuf Atta, Putla Sudarsanam, Suresh K. Bhargava, and Sharifah Bee Abd Hamid Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.5b02826 • Publication Date (Web): 03 Feb 2016 Downloaded from http://pubs.acs.org on February 4, 2016

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Energy & Fuels

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Highly Selective Hydrogenation of Biomass-

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Derived Furfural into Furfuryl Alcohol using a

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Novel Magnetic Nanoparticles Catalyst

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Ahmed Halilu†‡, Tammar Hussein Ali†, Abdulazeez Yusuf Atta‡, Putla

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Sudarsanam§, Suresh K. Bhargava§, Sharifah Bee ABD Hamid†*

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†

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Kuala Lumpur, Malaysia. ‡

9 10 11

Nanotechnology and Catalysis Research Center, (NANOCAT) Universiti Malaya, 50603

Department of Petrochemicals, National Research Institute of Chemical Technology (NARICT), P.M.B 1052, Nigeria.

§

Centre for Advanced Materials and Industrial Chemistry (CAMIC), School of Applied Sciences, RMIT University, Melbourne VIC 3001, Australia

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ABSTRACT: Designing efficient and facile recoverable catalysts is desired for sustainable

14

biomass valorisation. This work reports one-pot synthesis of a novel magnetic Fe(NiFe)O4-SiO2

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nanocatalyst for hydrogenation of biomass-derived furfural into valuable furfuryl alcohol.

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Various techniques were used to systematically analyse the physicochemical properties of

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Fe(NiFe)O4-SiO2 nanocatalyst. Vibrating sample magnetometer analysis reveals low coercivity

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of Fe(NiFe)O4-SiO2 (6.991 G) compared with that of Fe3O4-SiO2 (27.323 G), which is attributed

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to highly dispersed Ni species in Fe(NiFe)O4-SiO2 catalyst. HRTEM images indicated nanosized

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nature of Fe(NiFe)O4-SiO2 catalyst with an average diameter of ~14.32 nm. The Fe(NiFe)O4-

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SiO2 catalyst showed a superior BET surface area (259 m2/g), which is due to the formation of

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nanosized particles. Magnetic Fe(NiFe)O4-SiO2 nanocatalyst shows a remarkable performance

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with 94.3 and 93.5% conversions of furfural and ~100% selectivity of furfuryl alcohol at 90 oC

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and 20 H2 bar, 250 oC and 5 H2 bar, respectively. Using heptane as a solvent, the effect of

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temperature, pressure, reactant amount, and catalyst loading were investigated to optimize the

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reaction conditions. A probable mechanism via a non-hydrogen spillover route was proposed for

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the hydrogenation of furfural to furfuryl alcohol over magnetic Fe(NiFe)O4-SiO2 nanocatalyst.

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The efficiency of magnetic Fe(NiFe)O4-SiO2 nanocatalyst is attributed to highly dispersed nickel

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species, which play a key role in the dissociation of H2 into a proton and a hydride in the furfural

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hydrogenation. The superior performance of magnetic Fe(NiFe)O4-SiO2 nanocatalyst, along with

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the advantages of low cost and easy recoverability could make it a new appealing catalyst in

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various selective hydrogenation reactions.

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1. INTRODUCTION

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The world is presently facing detrimental environmental problems due to vast consumption of

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fossil fuels and associated global warming effects.1-3 The consumption of fossil fuels results in

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increasing levels of greenhouse gas (GHG) emissions; CO2 levels have increased from 284 ppm

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in 1832 to 397 ppm in 2013.3 Global GHG emissions are expected to rise by ~2.5% in 2015

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compared with 2013 levels. If this situation continues, global average temperatures will increase

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by 2.5-5.4 oC above pre-industrial levels by 2050. Concurrently, it is expected that the global

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production of petroleum will reach a maximum by 2020 and thereafter decay gradually.1 These

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growing concerns have motivated the researchers to search for alternative renewable feed-stocks

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for the production of fuels and chemicals.

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In this context, biomass is a potential feedstock alternative to fossil fuels due to its high

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abundance, biodegradability, and remarkable sustainability.4-6 Nature itself produces 170 billion

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metric tons of biomass per year by photosynthesis. Especially, lignocellulose contains large

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amount of biomass with three major components: cellulose (~35-50%), hemicellulose (~20-

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35%), and lignin (~10-25%). Thus, the production of fuels and chemicals from lignocellulose

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derivatives is an attractive way to overcome the negative impacts of fossil fuels.

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Furfural is one of the promising biomass platform chemicals that can be largely produced

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from acidic hydrolysis of hemicellulose.5,7-11 Several processes have been developed for the

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conversion of furfural into a number of valuable chemicals and fuels, such as furfuryl alcohol, 2-

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methylfuran,

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furfurylamine, 1,5-pentanediol, and so on. Among these, the production of furfuryl alcohol by

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selective hydrogenation of furfural has received a paramount interest because of many potential

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applications of furfuryl alcohol.10,12,13 For example, furfuryl alcohol is widely used in chemical

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industry, mainly for the production of foundry resins, synthetic fiber, farm chemicals, adhesives,

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and fine chemicals. In addition, furfuryl alcohol is used as a diluent for epoxy resins and as a

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solvent for phenol formaldehyde resins. In organic synthesis, furfuryl alcohol is a valuable

2-methyltetrahydrofuran,

tetrahydrofurfuryl

alcohol,

cyclopentanone,


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feedstock for the production of tetrahydrofurfuryl alcohol and 2,3-dihydropyran. Moreover, it is

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a key intermediate for the synthesis of lysine, vitamin C, lubricants, and plasticizers.

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In industry, furfuryl alcohol is obtained by hydrogenation of furfural with copper

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chromite catalysts, operating between 130 and 200 °C, at pressures up to 30 bar.12 The main

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drawback of copper chromite catalysts is the toxic nature of chromium oxides, which is highly

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undesirable from the viewpoints of 12 Green Chemistry Principles. Alternatively, a variety of

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precious and non-precious metal catalysts including Pt, Ru, Pd, Co, Cu and Ni dispersed on

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metal oxide supports have been investigated for the hydrogenation of furfural to furfuryl

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alcohol.12-18 However, the application of higher metal loadings, the use of drastic reaction

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conditions, and more importantly, difficulties in recovery and reuse of the catalysts in the above-

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mentioned works are major challenges in the hydrogenation of furfural to furfuryl alcohol.

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Furthermore, the developed catalysts must exhibit a prominent role in the transformation of C

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(Sp2)-O carbonyl carbon of furfural into stable C (Sp3)-OH carbon of furfuryl alcohol. These

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implications provide numerous opportunities to develop cheap, promising, and easy recoverable

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catalysts for efficient hydrogenation of furfural to furfuryl alcohol.

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The present work has been undertaken against the above background. A novel magnetic

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Fe(NiFe)O4-SiO4 nanoparticles catalyst was developed using a one-pot synthesis methodology at

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room temperature. In recent times, the application of magnetic nanoparticles in heterogeneous

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catalysis is growing tremendously due to the combined nanoscale and magnetite properties.19,20

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Nanosized catalysts exhibit a number of unique properties, such as high surface area, favorable

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electronic properties, and superior redox properties, which are significantly different from the

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bulk counterparts.21-22 Owing to remarkable separation properties, magnetic catalysts offer a

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promising option that can meet the requirements of high accessibility with easy recoverability for

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various applications in heterogeneous catalysis.19,20 As a result, filtration or centrifugation step,

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thus tedious workup for the separation of reaction mixture from the catalyst can be avoided in

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several catalytic reactions. These beneficial properties of magnetic nanoparticles can contribute

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to achieve better results in the transformation of biomass derivatives into valuable chemicals and

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fuels. Hence, in the present study the catalytic performance of magnetic Fe(NiFe)O4-SiO4

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nanoparticles catalyst was investigated for the hydrogenation of biomass-derived furfural into

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furfuryl alcohol. A number of analytical techniques have been used to systematically


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characterize the physical, chemical, redox, magnetic, and morphological properties of

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Fe(NiFe)O4-SiO4 catalyst. To optimize the reaction conditions for furfural hydrogenation, the

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effect of reaction temperature, pressure, catalyst amount, and reactant concentration using

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magnetic Fe(NiFe)O4-SiO4 nanocatalyst was investigated with heptane as a solvent. With the

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help of H2-TPR and GC-MS studies, a probable mechanism via a non-hydrogen spillover route

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was proposed for furfural hydrogenation over magnetic Fe(NiFe)O4-SiO4 nanoparticles catalyst.

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The developed magnetic Fe(NiFe)O4-SiO4 nanoparticles catalyst can also be efficiently used for

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any hydroprocessing reaction because of its superior reducibility nature and remarkable magnetic

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capacity.

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2. EXPERIMENTAL

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2.1. Materials. All chemicals were purchased from Merck Millipore and Chemo-lab

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Malaysia. The reactants used were ethanol (Riendemann Schmidt chemicals, 99.8w/w%),

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furfural (R&M, 99w/w%), nickel (II) nitrate hexahydrate (Sigma-Aldrich, ≥ 99.0w/w%),

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iron III chloride hexahydrate (R&M, 99.0w/w %), iron II chloride tetrahydrate (R&M,

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99w/w%), acetone (Merck Millipore), and aqeuous ammonia solution (Riendemann

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Schmidt chemicals, 25%).

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2.2. Catalyst Preparation. A facile co-precipitation method was used to synthesize magnetite

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Fe(NiFe)O4-SiO2 nanoparticles as shown in Figure 1.23 In a typical procedure, magnetic

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nanoferrite (Fe3O4) was generated in-situ at room temperature by precipitating the aqueous

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solutions of FeCl3·6H2O and FeCl2·4H2O in the ratio of 3:2 using aq. NH3 solution at pH ~10.

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The solution was stirred at 600 rpm for 1 h followed by the addition of 15 wt.% TEOS and then,

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stirring was continued for 24 h. Afterwards, an aqueous solution of nickel nitrate (98 wt.%) was

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added drop wise to the above solution and then pH was adjusted again to ~10. The mixture

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solution was then stirred at 600 rpm for 12 h at room temperature. The resulting Fe(NiFe)O4-

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SiO2 catalyst was washed with deionized water and then with HCl solution to remove any –OH

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group and finally washed with acetone. The synthesized magnetic Fe(NiFe)O4-SiO2

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nanoparticles catalyst was dried at 60 °C with 1° C/min; starting from 28 °C in static

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environment overnight.


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Figure 1. One-pot synthesis of magnetic Fe(NiFe)O4-SiO2 nanoparticles catalyst.

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2.3. Catalyst Characterization. Thermal gravimetric and differential thermal analysis (TG-

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DTA) analysis of the dried Fe(NiFe)O4-SiO2 catalyst was performed using Perkin-Elmer with 10

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°C/min ramping. The magnetic properties of Fe(NiFe)O4-SiO2 and bulk NiO samples were

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measured using a Lakeshore 7400 series, 7407 model with 7 inch electromagnet vibrating sample

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magnetometer (VSM). The analysis was conducted at room temperature in the field of ±10 kOe.

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The N2 adsoprtion–desorption studies were carried out on Micrometrics TriStar II 3020

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adsorption apparatus using ASTM D 3663-03 test method. The Brunauer–Emmett–Teller (BET)

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surface area of the sample was calculated by utilizing the desorption data. The H2-temperature

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programmed reduction (H2-TPR) analysis was conducted on TPDRO 1100 series setup equipped

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with a thermal conductive detector. Approximately 50 mg of the Fe(NiFe)O4-SiO2 sample was

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heated up to 120 °C at a rate of 10 °C/min in N2 (20 mL/min) for 30 min to make it water free.

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The sample was then switched to a 25% H2/N2 (V/V, 20 mL/min) mixture and then cooled to

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room temperature. The measurements were carried out in aN2 environment at a programmed

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temperature up to 700 °C at a rate of 10 °C/min.

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Fourier transform infrared (FT-IR) spectra of Fe(NiFe)O4-SiO2, reference Fe3O4-SiO2,

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and NiO samples that are dispersed in KBr, were measured at 400-4000 cm-1 wavelength region

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using Bruker FTIR IFS 66/S with are solution of 4 cm-1. Raman measurements were carried out

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using Reinishaw InVia Raman spectroscope with 514 nm excitation sources of Ar+ laser and

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0.01Mv power output. X-ray fluorescence (XRF) analysis of the Fe(NiFe)O4-SiO2 sample was

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carried out on Bruker S4-Explorer X-ray fluorescence (1kW). Powder X-ray diffraction (XRD)

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studies were conducted using XRD Bruker D8 advance instrument. The diffraction peaks were


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obtained at 28 °C with Cu Kα radiation at X-ray wavelength (λ) of 1.5406 Ǻ. The Bragg’s angle

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range was set from 10 to 80° with a step size of 0.03° and an acquisition time of 1 s/step at 40 kV

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and 40 mA. The catalyst surface morphology was analyzed by a field emission scanning electron

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microscopy (FEI Quanta 400). High resolution transmission electron microscopy (HRTEM)

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analysis was performed on a JEOL JEM-3010.

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2.4 Catalyst activation

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The catalyst activation was done using CRD multiple parallel pretreatment system coupled with

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240 mg/capsule catalyst encapsulation unit. The unit capacity is 600 oC maximum, modulated

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via ESA VT60 temperature controller along with 5 bar maximum pressure controlled

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workstation. In each experiment, 60 mg of Fe(NiFe)O4-SiO2 magnetic nanoparticles catalyst was

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activated at 500 oC with the ramping of 1 oC/min for 3 h under 10 mL/min flow of H2. The

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activation condition in this case is in accordance with the reduction conversion factor obtained

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from TPR experiments using 50 mg Fe(NiFe)O4-SiO2 at ~448 oC max for ~1 h. Prior to the

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experiment, the gas lines were primed with N2 for 30 minutes to ensure air free environment.

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2.5. Catalytic Activity Studies. The activity of magnetic Fe(NiFe)O4-SiO2 nanocatalyst

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was investigated for the hydrogenation of furfural in an automated 100 mL (42 mm ID)

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capacity autoclave reactor made of Hast-alloy C 276 material by Cambridge reactor

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design Ltd. The reactor is made up of a mechanical stirrer with proportional integral (PI)

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pressure and temperature controllers together with a gas detector for a leak check. Before

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the commencement of reaction, H2 cylinder set at 30 bar dosing pressure was connected

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to the reactor. The reactor was sealed and purged with inert N2 and then H2 to exclude air.

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In a typical experiment, 60 mg of activated catalyst was placed in a catalyst bulb and

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fixed on the catalyst bulb holder. This was followed by loading into the reactor, 20% (v/v)

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furfural in heptane solvent. Afterwards, the reactor was heated and allowed for isothermal

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stabilization to different desired set point reaction temperatures and H2 pressures. After

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completion of the reaction, the autoclave was cooled to 35 °C and depressurized to

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atmospheric pressure. The products were collected for qualitative analysis using gas

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chromatography measurements on an Agilent 6890N with 5973 MSD, auto-sampler, and

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HP-5 capillary column (1.5µm×30m×530µm). Furthermore, the quantitative analysis was


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done on an Agilent 6890N (G154ON) GC-FID using DB-WAX 30m×0.530mm column.

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The conversion of furfural and products selectivity was calculated using the formulas:

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Conversion % =

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Selectivity % = ∑ × 100

( ) ( )

( )

× 100

(1) (2)

179 180 181

3. RESULTS AND DISCUSSION 3.1. TG-DTA Analysis. The TGA-DTG curves for 8.1800 mg Fe(NiFe)O4-SiO2 pre-

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activated catalyst are shown in Figure 2. As shown in the figure, the total weight loss over

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the temperature range from 37 to 700 oC was found to be ~5.8505%, which is equal to

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0.4034 mg. However, the first weight loss peak over the temperature range of 37-180 oC

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might be due to the loss of residual water present on the catalyst surface. The noticed

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sharp weight loss at around 370 oC can be assigned to dissociation of (NO3)2 from

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Ni(NO3)2 precursor. The last weight loss observed in the range of 450-550 oC indicates

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the dissociation of chlorides from FeCl2 and FeCl3. This thermo-chemical behaviour of

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the catalyst described by TGA curve was consistent with DTG curve (Figure 2). In

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conclusion, the prepared catalyst is stable (>93%) up to 700 °C because only 5.8505%

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weight loss was found from TG-DTA study.

192 193 194 195 196 197 198 199 200 201

Figure 2. TG-DTA analysis of magnetic Fe(NiFe)O4-SiO2 catalyst.


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3.2. Vibrating Sample Magnetometer (VSM) Analysis. One of the attractive features of

203

Fe(NiFe)O4-SiO2 nanoparticles catalyst is its magnetic anisotropy, which is significantly

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different from the conventional catalysts. For this, VSM analysis of Fe(NiFe)O4-SiO2 has

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been undertaken. Figure 3 presents the hysteresis measurement at room temperature in the

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applied field sweeping from -10 to 10kOe of reduced Fe(NiFe)O4-SiO2 nanoparticles

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catalyst. The obtained results indicate super-paramagnetic property of Fe(NiFe)O4-SiO2

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nanocatalyst. The saturation magnetization (Ms) of Fe(NiFe)O4-SiO2 catalyst was found

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to be 39.834 emu/g, whereas reference Fe3O4-SiO2 core-shell architecture exhibits at

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about 45.67 emu/g. This decrease in Ms indicates successful incorporation of Ni2+ at the

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octahedral OD site in the Fe(NiFe)O4-SiO2 inverse spinel structure. This is in good

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agreement with 5.8136 G coercivity of Fe(NiFe)O4-SiO2, which is significantly low

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compared with that of 27.323 G coercivity of reference Fe3O4-SiO2 (Figure 3c).

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Therefore, the decrease in Hc and Ms is a clear indication of distortion in

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magnetocrystalline anisotropy contribution by Fe3+ as a result of Ni2+ occupying

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octahedral Fe3+ sites. As a consequence, the displaced Fe3+ occupies the vacant octahedral

217

oxygen sites. However, the possibility of Ni2+ leaching in contrast to conventional ones

218

used for the similar application would be expected to very low due to the magnetic

219

interaction of Ni2+ and Fe3O4. These observations are good agreement with previously

220

published results.24 These results also reveal that the catalyst has no NiO (anti-

221

ferromagnetism as seen in the Figure 3b) impurities. This indicates that electronic

222

structure of all Ni2+ is perturbed to form a strong bond at the octahedral site in contrast to

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a conventional non-magnetic catalyst, in which the electronic structure of Ni2+ is barely

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perturbed upon adsorption. In the latter case, the active metals are typically physisorbed

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in the glory of metal support interaction effects only. Reduction in Hc and Mc is an

226

indication of Ni incorporation into the lattice structure of Fe3O4 dispersed in SiO2. It is

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interesting to mention that the catalyst has 0.5042 emu/g magnetic remenance (Figure 3c).

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This observation indicates that the Fe(NiFe)O4-SiO2catalyst has magnetic property even

229

at room temperature when no magnetic field is applied.

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Magnetization (emu/g)

60 40 20 0

Fe(NiFe)O4-SiO2 Hci = 5.1836 G, Ms = 39.834 emu/g Mr = 0.4558 emu/g Fe3O4-SiO2

(a)

Hci = 27.323 G, Ms = 45.611 emu/g Mr = 1.9097 emu/g

-20 -40 -1000 0 1000

-60 -10000

-5000

0

5000

10000

H(Oe)

231 232 0.15

Magnetization (emu/g)

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Energy & Fuels

(b) 0.10

Ms = 0.1183 emu/g

0.05 0.00 -0.05

Hci = 40.216 G

-0.10 -0.15

-500 -10000

233

NiO

Mr = 0.0112 emu/g

0

1000 0

10000

Applied Field (Oe)


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30 2.0 Magnetic Remenance (Mr) Coercivity (Hci)

(c)

1.5 20

1.0

10

Coercivity (G)

Magnetic remenance (emu/g)

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0.5

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Ni loading (wt %)

234 235

Figure 3. Super-paramagnetic hysteresis loops for (a) Fe(NiFe)O4-SiO2 catalyst, (b) bulk nickel

236

oxide and (c) effect of Ni loading on magnetic Remanence (Mr) and coercivity (Hci) of the

237

Fe(NiFe)O4-SiO2 catalyst.

238 239

3.3. FT-IR and Raman Analysis. FT-IR and Raman analysis presented in Figure 4a and

240

4b, respectively, revealed the chemical structure of magnetic Fe(NiFe)O4-SiO2

241

nanoparticles catalyst having 0.51 wt.% nickel loading. The wavenumbers noticed from

242

FT-IR and Raman spectra and mode assignment for the magnetic Fe(NiFe)O4-

243

SiO2nanocatalyst were presented in Table 1. As shown in Figure 4a, the bands centred at

244

~1082 and 808 cm-1 can be assigned to asymmetric and symmetric vibrations of -Si-O-Fe

245

silica, respectively. These values confirm the formation of amorphous silica matrix.25,26

246

The possible perturbation occurring at octahedral site in the inverse spinel structure due to

247

the replacement of Fe3+ by Ni2+ ions can be explained by red shifted Ni2+-O bands at 460

248

cm-1. Evidently, this observation can be confirmed with the standard FT-IR spectra of

249

NiO noticed at ~451.57, 428.55, 415.74 and 407.99 cm-1 (Figure 4a). Additionally, for an

250

iron inverse spinel structure, higher wavenumber (500-600 cm-1) bands and lower

251

wavenumber (450-385 cm-1) bands were noticed, which correspond to the vibration of O-

252

MTd-O at the tetrahedron site and stretching in the O-Most-O octahedron sites27-29; where

253

MTd and Most represent metal at tetrahedral and octahedral sites, respectively. Therefore,


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the observed bands at ~567 and 648 cm-1 for Fe(NiFe)O4-SiO2 were related to the

255

vibrations of O-FeTd-O at the tetrahedral. Conclusively, this analysis was able to reveal

256

the presence of silica matrix that serves as a shell to the core magnetite (Fe3O4). The

257

presence of Fe3O4 was also confirmed by the vibrations O-Fe3+Td-O and the noticed red

258

shifted O-Ni2+oct-O at 460 cm-1 suggests nickel incorporation on Fe3O4 at the octahedral

259

sites.

260 261

Raman technique is a structure-sensitive tool that can used to confirm the observations

262

noticed from FT-IR analysis of magnetic Fe(NiFe)O4-SiO2 nanocatalyst. The Raman

263

spectrum of the catalyst shows six Raman active modes; A1g, Eg, T2g (1), T2g (2), T2g (3)

264

and TO-LO, along with three indicative modes for silica (Figure 4b). T2g (3) mode

265

centred at 598 cm-1 is assigned to symmetric stretching of oxygen atoms along Ni-O

266

bonds in the octahedral coordination, and this is an indication of a high degree of

267

disorderliness in bond length. T2g (2) centred at 500 cm-1 is due to asymmetric stretching

268

of Fe (Ni) and O at the octahedral coordination. The reason for the formation of these

269

bands is that Ni2+ has higher ionic radius (0.69 nm) compared to Fe3+ (0.49 nm), thus

270

incorporation of Ni2+ into the Fe3O4 structure creates a local structural distribution in

271

Fe/Ni-O bond length. Therefore, T2g (2) and T2g (3) correspond to vibrations of the

272

octahedral group. T2g(1) centred at 240 cm-1 is due to translational movement of the

273

tetrahedral Fe3+ together with four oxygen atoms. A1g centred at ~718 cm-1 is due to

274

symmetric vibration of Fe-O along the tetrahedral coordination. Eg band centred at ~450

275

cm-1 is due to symmetric bending of oxygen with respect to the metal ion. The

276

Longitudinal and Transverse optical vibration (LO-TO) centred at 1310 cm-1 is due to Si-

277

O-Fe asymmetry vibration. However, the silica siloxane bridge has Raman features at

278

~800 cm-1. This complimented,also, with the broad band at ~1070 and ~915 cm-1 as

279

atypical characteristic of Si-O- and Si(-O-)2 functionalities. The observation of these

280

bands indicates perturbation due to the formation of Fe-O-Si as a result of more Si-OH

281

hydroxyl group’s consumption. The observed resultsobviously indicate strong tetrahedral

282

vibrational coupling of fayalite-like Fe3O4-SiO2. This corresponds to the X-ray diffraction

283

of Fe3O4-SiO2 at planes (200), (103), (240), (341) and (064) in Fe(NiFe)O4-SiO4 (Figure

284

7).


11

Energy & Fuels

285

Table 1. Wavenumbers noticed from FT-IR and Raman studies and mode assignment for

286

the magnetic Fe(NiFe)O4-SiO2 catalyst. FT-IR Tetrahedral Site

S/N

Wavenumber

Assignment

-1

Raman Octahedral Site

Wavenumber

Tetrahedral Site

Assignment

Wavenumber

-1

(cm )

Octahedral Site

Assignment

-1

(cm )

Wavenumber

Assignment

-1

(cm )

(cm ) 3+

1

-

-

460

Ni-O

240

- Fe -

500

Ni-O

2

-

-

-

-

718

Fe-O

-

-

3

567

O-Fe-O

-

-

800

O-Si-O

598

Ni-O

-

-

-

4

648

O-Fe-O

-

-

915

Si-O

5

808

O-Si-O

-

-

1070

Si(-O-)2

-

-

6

1082

Si-O-Fe

-

-

1310

Si-O-Fe

-

-

287 288 289 290 291 292 293 294 T2g(3)

(b)

295

A1g

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Eg TO-LO T2g(2) T (1) 2g

2000

1500

1000

500

Wavenumber (cm-1)

296


12

Page 13 of 32

297

Figure 4. (a) FTIR spectrum and (b) Raman spectrum of Fe(NiFe)O4-SiO2 sample prepared

298

through co-precipitation and thermal anealation at 500 oC for 3 hours.

299 300

3.4.

301

Fe(NiFe)O4-SiO2 catalyst based on the elemental composition. The obtained results are presented

302

in Figure 5 and Table 2. The obtained XRF data reveals the presence of Ni2+ (0.51 wt.%) and

303

Fe3+(k% of 40.44 wt.%) in the octahedral site. This is indexed at 2theta-scale of 49.1 and 52.7°,

304

respectively, in Figure 5. On the other hand, Fe3+ ((1-k) % of 40.4 wt.%) at the tetrahedral site is

305

indexed at 58.6°. The chemical composiiton of the catalyst

306

Fe40.44O40.94Si18.11Ni0.51.

307

X-ray Fluorescence Analysis. XRF analysis was done to establish the formula of

was found to be

Table 2. XRF elemental composition of Fe(NiFe)O4-SiO2 308 Total

Composition x = Ni %

y = Si %

z = Fe%

n = O%

0.51

18.11

40.44

40.94

309 100 310

Catalyst formula: Fe40.44O40.94Si18.11Ni0.51

311

140

Fe 3+Td

120 100

Sqr(Kcps)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

80

= 40.4 wt % O 40.9 wt %

60 40

Fe 3+Od Si 18.1 wt % Ni 2+Od

0.51 wt %

20 0 20

40

60

80

100

120

140

2Theta-Scale

312 313

Figure 5. XRF spectrum of Fe(NiFe)O4-SiO2 magnetic nanoparticle.

314


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 32

315

3.5. Evaluating the Integrity of Fe3O4Core, SiO2Shell, and Fe(NiFe)O4-SiO2 Catalyst in

316

terms of Their Reducibility. The H2-TPR results presented in Figure 6 confirm the integrity of

317

Fe(NiFe)O4-SiO2 catalyst for hydroprocessing reaction via a non-hydrogen spillover route. The

318

analysis was focused on the reduction of active metal Mn+ specifically Ni2+, and testing the

319

reducibility of metal oxide (Fe3O4 and SiO2) support materials. The H2-TPR profiles of

320

Fe(NiFe)O4-SiO2, SiO2, and Fe3O4 reveal that the cationic Si of SiO2 is non-reducible. Bulk

321

Fe3O4 shows a large peak at around 643 oC with the consumption of 2452 µmol/g, indicating the

322

conversion of Fe3O4 to FeO. Also, the inactivated Fe(NiFe)O4-SiO2 catalyst exhibited three

323

reduction peaks centred at 408, 448 and 611 oC while consuming 4972 µmol/g H2. This

324

observation suggests reduction of Ni2+ to Ni+, Ni+ to Nio and Fe3O4 to FeO, respectively. The

325

reduction temperature range for Ni2+ in Fe(NiFe)O4-SiO2 lies between 400-500 oC. Since SiO2 is

326

non-reducible metal oxide up to 700 oC and Fe3O4 is only reducible at >600 oC, spillover of

327

hydrogen over SiO2, Fe3O4 or Fe3O4-SiO2 at

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